1. Field of the Invention
The present invention relates to a traveling device suitable for use in a coaxial two-wheeled vehicle having two wheels disposed on an identical axial center line, for example. More particularly, the present invention proposes a traveling device that can support itself easily when not carrying a passenger and can be conveyed easily by being dragged.
2. Description of Related Art
In a conventional coaxial two-wheeled vehicle, attitude control is performed on the vehicle mainly in a pitch axis direction by detecting the tilt of the vehicle using a plurality of gyros or the like (see a related reference U.S. Pat. No. 5,971,091, for example).
Further, in a device for controlling respective wheels, a handle or a step that is constrained in a neutral position by the restoring force of a spring or the like is provided, an angle of absolute incline relative to the gravity axis thereof or an angle of relative incline relative to a base of the vehicle is detected, and a steering operation corresponding to the magnitude of the detected angle is realized (see a related reference Japanese Unexamined Patent Application Publication No. 2006-315666 (Kakinuma, U.S. patent application Ser. No. 11/402,975 filed on Apr. 13, 2006, Pub. No. US 2006/0260857 A1), for example).
However, neither U.S. Pat. No. 5,971,091 nor Japanese Unexamined Patent Application Publication No. 2006-315666 describe a technique with which a device can support itself when not carrying a passenger and be transported by being dragged easily, such a technique being the object of the invention according to the present application.
A coaxial two-wheeled vehicle such as that shown in FIGS. 11A and 11B, for example, is known as a vehicle that carries a person and travels on two wheels. FIG. 11A is a front view showing the constitution of a coaxial two-wheeled vehicle serving as a traveling device to which the present invention is applied, and FIG. 11B is a side view showing the constitution of the coaxial two-wheeled vehicle serving as the traveling device to which the present invention is applied. Note that in FIGS. 11A and 11B, the main overall constitution is substantially identical to that of the device illustrated in a related reference Japanese Unexamined Patent Application Publication No. 2006-315666.
In FIGS. 11A and 11B, two wheels 1L, 1R disposed in parallel are provided, and these wheels 1L, 1R are provided respectively with independent driving means (motors) 2L, 2R. The driving means 2L, 2R are connected by vehicle main bodies 3U, 3D divided into an upper side and a lower side. Although not shown in the drawing, a circuit device such as control means for controlling the tilt of the vehicle, which is detected by a sensor such as a gyro, and controlling driving of the driving means 2L, 2R in accordance with information such as the load on the vehicle, is provided in the vehicle main bodies 3U, 3D.
A step plate for carrying a driver is provided on an upper side of the vehicle main bodies 3U, 3D. The step plate is indicated by steps 4L, 4R divided into left and right sides, and these steps 4L, 4R are connected by a link mechanism (not shown) so as to be parallel at all times. A handle 5 is provided between the steps 4L, 4R. The handle 5 is provided at a predetermined forward tilt relative to the vehicle main bodies 3U, 3D, and the handle 5 is connected to the steps 4L, 4R by a link mechanism (not shown) such that a right angle is formed therebetween when the vehicle is seen from the front.
The specific constitution of a control device for this type of coaxial two-wheeled vehicle will now be described using the pattern diagram of a single wheel model shown in FIG. 12. Note that in an actual two-wheeled vehicle, the sensors of the step 4 are shared. Further, control of the motor 2 connected to the wheel 1 in the illustrated model is performed using independent control devices for the wheels 1L, 1R shown in FIGS. 11A and 11B.
In FIG. 12, pressure detection signals PS1, PS2, PS3, PS4 from a pressure sensor (not shown) installed in the step 4 and a table angle detection signal θ0 from an attitude sensor 8 constituted by a gyro sensor or an acceleration sensor connected to the step 4 are supplied to a central control device 91 provided in a control device 9. The detection signals PS1 to PS4 and θ0 and a table attitude command signal θREF [d (θREF)/dt] issued externally by a passenger or the like are then computed, whereupon a calculated rotation command ωref is supplied to a motor control device 92.
Further, the wheel 1 and motor 2 are connected via a decelerator 93, and the motor 2 is provided with a rotation angle detector 94. A rotor rotary angle position signal Θr from the rotary angle detector 94 is supplied to the motor control unit 92 in the control device 9. Thus, a drive current to be supplied to the motor 2, which is formed in accordance with the aforementioned rotary command ωref, is feedback-controlled, and as a result, driving of the wheel 1 is stabilized. Hence, the wheel 1 is driven with stability, and the driving thereof is controlled by the pressure detection signals PS1 to PS4 from the pressure sensor (not shown) and so on.
FIG. 13 shows mutual connection relationships in the system. In FIG. 13, the aforementioned pressure detection signals PS1 to PS4 and a roll axis angle detection signal PM from a roll axis angle detector (potentiometer) 12 provided in association with the handle 5, for example, are supplied to an attitude sensor circuit 13. A gyro sensor 21 and an acceleration sensor 22 are installed in the attitude sensor circuit 13. Accordingly, the aforementioned signals PS1 to PS4, the signal PM, a pitch angle ωp, a yaw angle ωyaw, and angle signals Ax, Ay, Az relating respectively to the X, Y and Z axes are extracted from the attitude sensor circuit 13.
These signals PS1 to PS4, PM, ωp, ωyaw, and Ax, Ay, Az are supplied to the central control device 91 in the control device 9. An operation signal from a power switch 14 provided on a grip portion of the handle 5, for example, is also supplied to the central control device 91. Hence, in the central control device 91, rotation commands ωref1, ωref2 for the left and right wheels 1L, 1R (not shown) are calculated and supplied to motor control units 92L, 92R. Further, signals from rotation angle detectors 94L, 94R are supplied to the motor control units 92L, 92R to drive the motors 2L, 2R.
Further, power from a battery 15 is supplied to a power circuit 95. 24V motor power, for example, is supplied to the motor control units 92L, 92R from the power circuit 95, and 5V control power, for example, is supplied to the attitude sensor circuit 13 and the central control device 91. Note that the power circuit 95 is provided with a power switch 16 for controlling power supply to each unit. As a result, the motors 2L, 2R are driven, and by driving the motors 2L, 2R, the wheels 1L, 1R are driven, thereby causing the coaxial two-wheeled vehicle to travel.
Incidentally, in this type of traveling device, as shown in FIGS. 14A and 14B, for example, a situation in which the device is dragged by the handle 5 while not carrying a passenger may arise. In such a case, if a motor (not shown) is connected to the wheel 1, resistance is generated in the rotation of the wheel 1 due to the influence of the decelerator and so on, even when torque is not generated in the motor. This resistance Ff is in inverse proportion to a diameter R of the wheel 1 when a frictional torque Tf is constant, and therefore, when the diameter is small, as shown in FIG. 14B, the resistance is much larger than when the diameter is large, as shown in FIG. 14A. Hence, in certain cases it may be impossible to drag the traveling device easily.
Furthermore, when the motor is not driven in the traveling device described above, the device cannot support itself. Therefore, when not carrying a passenger, then device is propped against a wall, or a dedicated holder or stand is used. When no such wall, holder, or stand is present, the device is laid on its side, and in all of these cases, the procedure is troublesome. In view of this, the applicant of the present application has proposed a technique for achieving self-support through drive-control of the motor (Japanese Unexamined Patent Application Publication No. 2007-336785), but this technique is problematic in that power consumption increases in the long term.
This application has been designed in consideration of these points, and the problems to be solved thereby are that in a conventional device, self-support cannot be achieved easily. Further, when an attempt is made to convey the device by dragging it, resistance increases dramatically, particularly if the diameter of the wheel is small, and therefore the device cannot be dragged easily.